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Every web server on the internet is assigned a unique address called an IP (Internet Protocol) address. This address is much like a telephone number - a unique number that lets other computers connect to a specific server. IP addresses are 4 bytes, or 32 bits. Each byte is called an "octet" and can be given a value between 0 and 255 so an IP address takes the form of 123.45.67.89. Theoretically, 32 bit IP addresses support more than 4 billion unique addresses but in reality the number is much less. Certain ranges are reserved for particular uses so the number of available IP addresses is limited. Web hosts get around this limitation with shared hosting and virtual servers. To avoid having to use a single server for each web site, shared hosting lets a single server host many web sites. Each site has the same IP address (the one assigned to the server itself) but a unique domain name (eg. mydomain.com). The current IP address numbering system is version 4 (IPv4) and there is a new system called version 6 (IPv6). This new version will allow for 128 bit addresses which will greatly expand the number of available addresses. Because the internet is currently built around the IPv4 standard, it will take a number of years to upgrade the infrastructure to support this new format. Shared hosting helps to solve the problem of a limited number of IP addresses for an ever-expanding number of website, but we also need to consider that every computer connected to the internet is also assigned an IP address. To avoid having to assign a unique IP address to every computer that connects to the internet, most internet providers use system called dynamic IP. They are given a range of available addresses and when you connect, you are assigned one of these numbers. When you disconnect, that number goes back into the "pool" and someone else will get it when they connect. This dynamic IP system is one of the reasons it's not usually feasible to host a website on your home computer. Because your address can change any time, it is difficult to keep your domain and your IP address properly associated. John Lenaghan writes about the best web hosting solution for businesses, and other website hosting topics on the Hosting Report website. Find out more at http://www.hostingreport.org
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